linux-kernel - Re: [PATCH v3] proc/ksm: add ksm stats to /proc/pid/smaps

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Message-ID: <886b6a56-8acb-e975-b5f3-d8098a2285ab@redhat.com>
Date:   Fri, 18 Aug 2023 16:35:46 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Stefan Roesch <shr@...kernel.io>, kernel-team@...com
Cc:     akpm@...ux-foundation.org, linux-fsdevel@...r.kernel.org,
        hannes@...xchg.org, riel@...riel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3] proc/ksm: add ksm stats to /proc/pid/smaps

On 17.08.23 18:23, Stefan Roesch wrote:
> With madvise and prctl KSM can be enabled for different VMA's. Once it
> is enabled we can query how effective KSM is overall. However we cannot
> easily query if an individual VMA benefits from KSM.
> 
> This commit adds a KSM section to the /prod/<pid>/smaps file. It reports
> how many of the pages are KSM pages. The returned value for KSM is
> independent of the use of the shared zeropage.
> 
> Here is a typical output:
> 
> 7f420a000000-7f421a000000 rw-p 00000000 00:00 0
> Size:             262144 kB
> KernelPageSize:        4 kB
> MMUPageSize:           4 kB
> Rss:               51212 kB
> Pss:                8276 kB
> Shared_Clean:        172 kB
> Shared_Dirty:      42996 kB
> Private_Clean:       196 kB
> Private_Dirty:      7848 kB
> Referenced:        15388 kB
> Anonymous:         51212 kB
> KSM:               41376 kB
> LazyFree:              0 kB
> AnonHugePages:         0 kB
> ShmemPmdMapped:        0 kB
> FilePmdMapped:         0 kB
> Shared_Hugetlb:        0 kB
> Private_Hugetlb:       0 kB
> Swap:             202016 kB
> SwapPss:            3882 kB
> Locked:                0 kB
> THPeligible:    0
> ProtectionKey:         0
> ksm_state:          0
> ksm_skip_base:      0
> ksm_skip_count:     0
> VmFlags: rd wr mr mw me nr mg anon
> 
> This information also helps with the following workflow:
> - First enable KSM for all the VMA's of a process with prctl.
> - Then analyze with the above smaps report which VMA's benefit the most
> - Change the application (if possible) to add the corresponding madvise
> calls for the VMA's that benefit the most
> 
> Signed-off-by: Stefan Roesch <shr@...kernel.io>
> ---
>   Documentation/filesystems/proc.rst | 4 ++++
>   fs/proc/task_mmu.c                 | 5 +++++
>   2 files changed, 9 insertions(+)
> 
> diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
> index 7897a7dafcbc..d5bdfd59f5b0 100644
> --- a/Documentation/filesystems/proc.rst
> +++ b/Documentation/filesystems/proc.rst
> @@ -461,6 +461,7 @@ Memory Area, or VMA) there is a series of lines such as the following::
>       Private_Dirty:         0 kB
>       Referenced:          892 kB
>       Anonymous:             0 kB
> +    KSM:                   0 kB
>       LazyFree:              0 kB
>       AnonHugePages:         0 kB
>       ShmemPmdMapped:        0 kB
> @@ -501,6 +502,9 @@ accessed.
>   a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
>   and a page is modified, the file page is replaced by a private anonymous copy.
>   
> +"KSM" shows the amount of anonymous memory that has been de-duplicated. The
> +value is independent of the use of shared zeropage.
> +
>   "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
>   The memory isn't freed immediately with madvise(). It's freed in memory
>   pressure if the memory is clean. Please note that the printed value might
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 51315133cdc2..f591c750ffda 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -396,6 +396,7 @@ struct mem_size_stats {
>   	unsigned long swap;
>   	unsigned long shared_hugetlb;
>   	unsigned long private_hugetlb;
> +	unsigned long ksm;
>   	u64 pss;
>   	u64 pss_anon;
>   	u64 pss_file;
> @@ -452,6 +453,9 @@ static void smaps_account(struct mem_size_stats *mss, struct page *page,
>   			mss->lazyfree += size;
>   	}
>   
> +	if (PageKsm(page))
> +		mss->ksm += size;
> +

Did you accidentally not include handling of the KSM-shared zeropage?

Or did I misinterpret "independent of the use of the shared zeropage."

-- 
Cheers,

David / dhildenb